1. Field of the Invention
The present invention relates to a substrate carrying apparatus, a substrate carrying method, and a coating and developing apparatus equipped with the substrate carrying apparatus, for carrying substrates having subjected to a process in which a liquid remains on a periphery of the rear face of each substrate, such as a dipping exposure process.
2. Background Art
Conventionally, in a photo-resist process, which is one of the processes for manufacturing semiconductors, semiconductor wafers (hereinafter referred to as wafers) are coated with a resist on their surfaces; and the resist is exposed to light through a predetermined pattern, and thereafter a developing liquid is supplied to the wafers to develop and form a resist pattern. This process is performed using a system in which an exposure machine is connected to a processing block of a coating and developing apparatus generally including a coating unit and a developing unit.
Transferring wafers from the processing block to the exposure machine or from the exposure machine to the processing block is performed via an interface residing between the processing block and the exposure machine. In the interface, for example, two substrate carrying apparatuses are provided.
In recent years, an exposure technique, referred to as a dipping exposure process, has been studied for the purpose of enhancing resolution of exposure due to the need for micromachining and thin-film forming of device patterns. What is meant by a “dipping exposure process” is an exposure process in which a liquid layer, such as a layer of ultra-pure water, is first formed for transmitting light through the layer onto a surface of a wafer, and the wafer surface is then irradiated with light generated from a light source through the liquid layer, whereby a predetermined circuit pattern can be transferred to a resist on the wafer surface. More specifically, if, for example, ArF is used as a light source for performing the exposure process, the wavelength of light generated from the light source is 193 nm in the air, but becomes substantially 134 nm in water. Thus, in this technique, a high resolution exposure process can be performed by utilizing such a phenomenon that the wavelength of light becomes short in water.
An exposure apparatus adapted to perform such a dipping exposure process is briefly explained with reference to FIG. 12. An exposure means 1 facing a wafer W with a gap is arranged above the wafer W held in a horizontal position by a holding means (not shown). A lens 1a is provided in a central distal end of the exposure means 1, and a supply port 1b for supplying a solution, for example, pure water, for forming a liquid layer on the surface of the wafer W and a suction port 1c for suctioning and recovering the pure water supplied to the wafer W are arranged around the outer periphery of the lens 1a. In this case, by supplying pure water to the surface of the wafer W from the supply port 1b while recovering pure water from the suction port 1c, a liquid film or layer (pure water film) can be formed between the lens 1a and the surface of the wafer W. Thereafter, light is emitted from a light source (not shown), passes through the lens 1a, and is then transmitted through the liquid film onto the wafer W, whereby a predetermined pattern can be transferred to a resist.
Subsequently, in the state where the liquid film is formed between the lens 1a and the wafer W, the exposure means 1 is moved sliding on the wafer W so that the exposure means 1 can be located at a position corresponding to a next transfer region (shot region). Thereafter, by repeating the irradiating operation with light, the circuit pattern can be transferred successively to the surface of the wafer W.
In a wafer just after being subjected to such a dipping exposure process, a liquid, for example, pure water, used for the exposure process travels, as shown in FIG. 3, from the surface through the peripheral end face to a portion on the rear face, thus forming a liquid drop 11. The extent in which the liquid drop 11 is attached to the rear face of the wafer W is ranging from the peripheral end of the wafer W to a 2 mm inside position. In FIG. 13, reference numeral 12 denotes a resist film formed on the wafer W.
FIG. 14 shows a situation at a front end portion of a carrying arm which has been studied to carry the wafer W just after being subjected to the aforementioned dipping exposure process. In the drawing, reference numeral 13 designates an arm body and reference numeral 14 denotes a nail portion provided at a front end portion of the arm body 13. To the nail portion 14, a restricting portion 15 for controlling the position of the periphery of the wafer W is provided. A raised restricting face 15a disposed inside the restricting portion 15 is configured to face the peripheral end face of the wafer W, which is placed on the arm body 13, and adapted to control the position of the periphery of the wafer W. At the lower end of the restricting face 15a, a supporting face 16 for supporting the wafer W is provided in succession, for example, in a generally horizontal direction. On the further inside of the supporting face 16 provided in the nail portion 14, a downwardly inwardly inclined face 17 is provided.
The arm body 13 is operated such that it can scoop up the wafer W placed on, for example, a stage (not shown) provided in an exposure apparatus so as to place the wafer W on the supporting face 16 (FIGS. 14(a), 14(b)). In FIG. 14(b), the length from the peripheral end of the wafer W contacting with the supporting face 16 to the front end of the supporting face 16 is, for example, about 1 mm. When the wafer W is placed on the supporting face 16 in such a manner, the liquid forming the liquid drop 11 at the lower periphery of the wafer W is forced to move to the corner between the supporting face 16 and the restricting face 15a. Thereafter, when the wafer W is separated from the arm body 13 as shown in FIG. 14(c), the liquid 18 forced to move to the corner tends to remain attached to the corner due to the surface tension. Thus, by repeating such an operation, the liquid 18 remaining at the corner is gradually accumulated.
However, if the remaining liquid 18 is accumulated in such a manner, either by impact occurring when the arm body 13 receives a next wafer from the exposure apparatus, or by vibration of the arm body 13 carrying a next wafer after having received it, the liquid 18 may tend to scatter into the air and be attached again to the next wafer W. If water drops are attached to the surface of the wafer W, the temperature of each site to which the water drop is attached or of another site in which a water mark is produced becomes different from that of other sites upon a subsequent heating process, resulting in deterioration of the uniformity in the resist pattern face. Although it may be possible to wash the wafer W prior to heating, it is quite difficult to remove micro-water drops. Therefore, it is necessary to avoid the attachment of water drops to the wafer W during the carrying operation.
Furthermore, there may be a risk that the wafer W sticks to the arm body 13 due to the surface tension of the liquid 18, resulting in jumping of the wafer W from the arm body 13 upon transferring the wafer W toward the processing block, thereby causing a carrying error.
In addition, once the carrying operation of the wafer W in the developing apparatus is stopped, the liquid 18 accumulated at the corner may tend to be dried and produce particles 10 as shown in FIG. 15(a). These particles 10 may be produced by absorption of constituents in the air into the liquid 18 or by elution of components constituting the arm body 13 into the liquid 18 which is pure water. However, the principle of occurrence of such particles is now under investigation. Thereafter, when the carrying operation of the wafer W is restarted by the arm body 13, either by impact occurring when the arm body 13 receives a next wafer W from the exposure apparatus, or by vibration of the arm body 13 carrying a next wafer after having received it, the particles 10 may also tend to scatter into the air as shown in FIG. 15(b) and be transferred to the next wafer W. It should be noted that though a substrate holding means provided in a coating and developing apparatus is described in Patent Document 1, a countermeasure for addressing the aforementioned problem which may occur upon the introduction of the dipping exposure process is not covered therein.
Cited Patent Document:
    Patent Document 1: TOKUKAIHEI No. 11-243133